1. Field of the Invention
The present invention relates to a preform neck crystallization method and the like.
2. Description of the Related Art
A wide-neck (wide-mouth) container has a structure in which the ratio of the outer diameter of the neck to the outer diameter of the body is larger than that of a narrow-neck (narrow-mouth) container (e.g., polyethylene terephthalate (PET) bottle) that is widely used as a beverage container. For example, a container having a neck outer diameter of 45 mm or more is generally referred to as “wide-neck container”. Since the wide-neck container allows easy removal of the contents, the wide-neck container has been used as a solid (e.g., jam) container in addition to a liquid container.
The wide-neck container normally employs a top-side seal structure (i.e., the top side of the neck is sealed using a cap). Therefore, deformation of the top side of the neck must be as small as possible in order to improve the seal-tightness.
In particular, when the wide-neck container is subjected to a high-temperature filling operation, it is necessary to crystallize the neck (i.e., increase the density of the neck) so that the neck exhibits heat resistance. When crystallizing the neck, the volume of the neck decreases along with an increase in density, so that deformation of the neck easily occurs. It is necessary to prevent a situation in which such deformation adversely affects the top side of the neck.
Japanese Utility Model Registration No. 3064403 and JP-A-2006-297775 disclose a neck crystallization method that heats the neck from the inner side and the outer side, and JP-A-11-152122, JP-A-2004-26201, and JP-A-2004-131175 disclose deformation of the neck of a narrow-neck container.
In Japanese Utility Model Registration No. 3064403 and JP-A-2006-297775, a core is inserted into the neck of a narrow-neck preform to heat the neck of the narrow-neck preform from the inner side and the outer side. In Japanese Utility Model Registration No. 3064403, a second heat source (22) that heats a thermal conductor (21) that is part of a core that extends outward from the neck is provided in addition to a first heat source (12) that heats the neck from the outer side, and heat from the second heat source (22) is transmitted to the core to heat the neck from the inner side (see FIG. 7). In JP-A-2006-297775, the second heat source (22) disclosed in Japanese Utility Model Registration No. 3064403 is omitted, and the thermal conductor (21) disclosed in Japanese Utility Model Registration No. 3064403 is replaced with a fin (12a) to heat the neck from the outer side. Heat retained by the internal heating core is dissipated through the fin (12a) to achieve the balance between internal heating and external heating (see FIG. 4).
However, when using the method that supplies heat to the core (Japanese Utility Model Registration No. 3064403) or the method that promotes dissipation of heat from the core (JP-A-2006-297775), the neck crystallization temperature predominantly depends on the temperature of the heat source provided outside the neck (i.e., internal heating using the core is subsidiary). Japanese Utility Model Registration No. 3064403 focuses on the temperature gradient between the inner wall and the outer wall of the neck (see FIGS. 5 and 6), and JP-A-2006-297775 maintains the temperature between the inner wall and the outer wall of the neck constant by combining rapid external heating and heat dissipation using the fin (see paragraph 0058). However, Japanese Utility Model Registration No. 3064403 and JP-A-2006-297775 are silent about a change in temperature with time from room temperature to the crystallization temperature.